The formation of polymers by anionic polymerization is well known in the art. These polymers are typically achieved by the formation of the living polymer that reacts with monomeric segments. Completion of this polymerization process is generally achieved by terminating this living polymer. In other words, the living end is reacted with a terminating agent that quenches the polymerization process. Many terminating agents, which also include coupling or linking agents, are known in the art.
When conducting polymerizations on a commercial basis, it is important to utilize process conditions and components which will allow the molecular weight of the end products to be narrowly and reproducibly defined. The characteristics of a given polymer and its usefulness are dependent, among other things, upon its molecular weight. Hence, it is desirable to be able to predict with some certainty the molecular weight of the end product of the polymerization.
In the art, it is desirable to produce elastomeric compounds exhibiting reduced hysteresis characteristics. Such elastomers, when compounded to form articles such as tires, power belts and the like, will show an increase in rebound, a decrease in rolling resistance and will have less heat build-up when mechanical stresses are applied.
A major source of hysteretic power loss has been established to be due to the section of the polymer chain from the last cross link of the vulcanizate to the end of the polymer chain. This free end cannot be involved in an efficient classically recoverable process, and as a result, any energy transmitted to this section of the cured vulcanizate is lost as heat. It is known in the art that this type of mechanism can be reduced by preparing higher molecular weight polymers which will have fewer end groups. However, this procedure is not useful because processability of the rubber with compounding ingredients and during shaping operations decreases rapidly with increasing molecular weight.
It is also known in the art to reduce hysteresis loss by providing the end of the polymeric chain with a functional unit that will serve to anchor the free end and reduce hysteresis loss. For example, U.S. Pat. No. 5,552,473 to Lawson et al., teaches polymers initiated with one functional group and terminated with a second functional group. As a result, an elastomer is produced having greater affinity for compounding materials, such as carbon black, thereby reducing hysteresis loss.
More specifically, it is know in the art to employ amine containing compounds to terminate, and/or initiate, polymerization reactions and thereby provide the polymer with a functional unit suitable for reducing hysteresis loss. Based on the molecular structure of these amine containing compounds, the functional group is tethered to the polymeric chain via a nitrogen atom. Such compounds are generally described by Richards et al. in British Polymer Journal, volume 16, page 117, 1984; Charlier et al. in Macromolecules, volume 23, page 1831, 1990; and Ueda et al., Macromolecules, volume 23, page 939, 1990. As a result, these compounds have the potential of losing the incorporated amine through thermal, chemical or mechanical degradation.
Thus, there is a need in the art for improved amine containing anionic polymerization initiators and/or terminators.